Hmm.. AFAIK you can delete your G+ profile and still keep your Gmail - https://support.google.com/plus/answer/1044503?hl=en
Except if you went with the "sign in with Facebook" option for third party apps.
You'll be losing saved games in Farmville for instance (maybe no big deal to you but still friction for some).
I would lose my Endomono fitness tracking account, that would make me pause.
I'm sure there are many others, just like for Google+.
So here is the elephant in the room "privacy allegation": if I mess up and make a drunk post on Facebook, I can purge the entire profile and move on. Gmail, however, and a host of associated tools have been critical for my jobs and business for many years. If i make a stupid drunk post on Google+, I don't even want to think how and what parts of my job and business it might affect, so in the foreseeable future I'm staying miles away from anything "social Google".